1. Field of the Invention
The present invention relates to a ball point pen. More specifically, the invention relates to a ball point pen in which a spring for pressing forward a ball is provided within a tip body. In the description of the invention to be given hereunder, the word xe2x80x9cfrontxe2x80x9d indicates the tip-body side of the ball point pen, and the word xe2x80x9crearxe2x80x9d indicates the ink-storage-tube side of the ball point pen.
2. Description of the Related Art
This type of ball point pen is disclosed in Japanese Utility Model No. 2577544, for example. In the ball point pen, a spring for pressing forward a ball comprises a coil part and a straight part. The straight part for pressing the ball forward is inserted into the tip body. The coil part for generating a resilient force is located to the rearward of the tip body. In the publication, the rear end of the coil part is engaged with and stopped by a spring receiving seat as a separate member.
Thus, the conventional ball point pen needs another separate member, such as a spring receiving seat, for engaging and stopping the rear end of the spring. This results in increasing the time and labor of the assembling work, and the number of required component parts. Hence, the cost to manufacture is increased, viz. it is difficult to provide products at low cost to the market.
Further, the conventional ball point pen suffers from the following problem. In the step for assembling the spring into the tip body, the front end of the coil part that has been inserted into the tip body is brought into contact with the rear surface of the ball, and at the same time, the coil part is compressed. The front end of the straight part is caught at the rear end of the ball receiving seat. The spring is assembled into the ball point pen structure in a state that the front end of the straight part is brought into improper contact with the rear surface of the ball. This causes a problem of defective assembling of the spring.
In a case where the tip body is of the type in which a ball is held at the front end of a straight thin tube made of metallic material (called a needle tip), the ink flowing elongated hole within the thin pipe is small in diameter. Accordingly, it is difficult to form a centering guide surface in a rear part of the ball receiving seat. The front end of the straight part of the spring is caught at the rear face of the ball receiving seat, and defective assembling is likely to occur. In a case where the tip body is of the type in which the ball receiving seat is formed by inward press deforming, the rear face of the ball receiving seat is not a smooth slanted surface, the front end of the straight part is caught at the rear face of the ball receiving seat and sometimes fails to come in contact with the rear surface of the ball.
Accordingly, It is an object of the present invention to provide a ball point pen which does not need an additional separate member with and at which the spring is held and to succeed in reducing the time and labor for the assembling and the number of required component parts, and the cost to manufacture. It is an another object to provide a ball point pen to enable the front end of the straight part to be brought into reliable contact with the rear surface of the ball without the defective assembling.
In order to achieve the above objects, a ball point pen as a first aspect of the invention comprising:
a holder including a front portion;
a tip body including
a rear end fastened to the front portion of the holder; and
a front end having a tip apex edge portion being formed inwardly curved and a ball receiving seat located rearwardly of the tip apex edge portion;
a ball rotatably held between the tip apex edge portion and the ball receiving seat; and
a spring disposed within the tip body and the holder for pressing the ball toward an inner surface of the tip apex edge portion, the spring comprising
a straight part passing through inside of the tip body; and
a coil part integrally joined to a rear end of the straight part, and disposed within the holder, wherein a protrusion is integrally formed on an inner surface of the holder, and the coil part is held on the protrusion in compressed state.
In the ball point pen thus constructed, the coil part 7 is held on the protrusion 4. With this feature, there is no need of using an additional separate member with and at which the spring is held. This feature reduces the time and labor of assembling, and the cost to manufacture.
As a second aspect of the invention, the coil part comprised a first coil part 72 connected to a rear end of the straight part and a second coil part. The second coil part 71 may be provided on the rear end of the coil part 7, and the second coil part 71 is held on the protrusion 4 in the ball point pen 1.
When comparing with a case where the whole coil part is held on the protrusion 4 on the inner surface of the holder 3 (viz., no second coil part 71 is provided on the coil part 7), only the second coil part 71 is held on the protrusion 4 on the inner surface of the holder 3. Therefore, the stroke that the second coil part 71 is held on the protrusion 4 is reduced to make, the mounting work simple. With the feature of the length reduction of the stroke that the second coil part 71 is held on the protrusion 4, damage of the protrusion 4 is considerably lessened when the coil part 7 is held the protrusion 4.
As the third aspect of the invention, in the ball point pen 1 a length (as viewed in the axial direction) from the front end of the straight part of the spring to the front end of the second coil part, when the spring is in uncompressed state, may be larger than a length (as viewed in the axial direction) from the rear end of the ball to the protrusion on the inner surface of the holder.
In a following explanation the length (as viewed in the axial direction) from the front end of the straight part of the spring to the front end of the second coil part, when the spring is in uncompressed state, is A. The length (as viewed in the axial direction) from the rear end of the ball to the protrusion on the inner surface of the holder is also described as B in following explanation.
The tip body 2 which rotatably holds the ball 23 in the ball embracing part located at the front part thereof, is fastened to the front part 31 of the holder 3. The spring 5 is inserted into the holder 3through its rear end opening. As shown in FIG. 2, during the process to insert the spring 5 into the tip body 2 and the holder 3, the spring 5 is temporarily inserted by a small force (e.g., dropping) through the rear end opening of the holder 3 in a state that straight part 6 is directed forward.
At this time, because of the construction (A greater than B) the second coil part 71 of the rear end of the coil part 7 does not climb over the protrusion 4 on the inner surface of the holder 3 and hence the second coil part 71 has not held on the protrusion 4 yet. Accordingly, the coil part 7 is not yet compressed. Accordingly, the front end of the straight part 6 is axially movable and also in radial directions. Even if the front end of the straight part 6 is caught at the rear end face of the ball receiving seat 22 and is not in contact with the rear surface of the ball 23, the front end of the straight part 6 may easily and appropriately be brought into contact with the rear surface of the ball 23 by applying a small force (e.g., vibration) thereto. After the front end of the straight part 6 is appropriately brought into contact with the rear surface of the ball 23, the second coil part 71 is held on the protrusion 4 on the inner surface of the holder 3. As a result, the coil part 7 is in a compressed state.
Accordingly, there is no chance that the front end of the straight part 6 is caught by the ball receiving seat 22, and the spring 5 is assembled while it is brought into improper contact with the rear surface of the ball 23. The front end of the straight part 6 is brought into reliable contact with the rear surface of the ball 23, thereby completely suppressing occurrence of the defective assembling.
As forth aspect of the invention, the tip body preferably comprises a straight, metal thin tube in the ball point pen.
The features of the first and forth aspect of the invention operate to produce the following effect: a ball point pen of the type in which the spring 5 for pressing the ball 23 forward is disposed within the tip body 2 as a straight, metal thin tube (called a needle tip) is produced at low manufacturing cost and marketed at low price.
The features of the second and forth aspect of the invention operate to produce the following effect: a ball point pen of the type in which the spring 5 for pressing the ball 23 forward is disposed within the tip body 2 as a straight, metal thin tube (called a needle tip) is produced at lower manufacturing cost and marketed at lower price.
In a case where the tip body 2 is a straight thin tube made of metallic material, the inner diameter of the ink flowing elongated hole 35 located behind the ball embracing part is usually substantially equal to or smaller than the diameter of the ball embracing part. Accordingly, it is difficult to form a centering guide surface in the ink flowing elongated hole 35. The front end of the straight part 6 of the spring 5 is caught at the rear face of the ball receiving seat 22, and defective assembling is likely to occur. Because of this, the construction (A greater than B) effectively operates, so that the front end of the straight part 6 is brought into reliable contact with the rear surface of the ball 23, thereby completely suppressing occurrence of the defective assembling.
In the tip body 2 as a straight, metal thin tube, usually, the rear outer surface of the tip apex edge part 21 is not tapered. The ball receiving seat 22 of the tip body 2 comes in two varieties: a ball receiving seat 22 formed by inwardly pressing and a ball receiving seat 22 formed by cutting.